A follow-on post from yesterday’s, on a Friends of the Earth ‘Bees in danger’ meeting I went to on Wednesday night. Our second talk of the evening was from Rob Mitton, an MSc student from Royal Holloway College, who explained scientific findings so far on the effects of neonicotinoids on bees.
Neonicotinoids are a class of neuro-active insecticides chemically related to nicotine. They work as neural agonists, building up in the brain of insects and exciting too many neural paths, leading to paralysis and death. They have been introduced fairly recently, after their development began with work in the 1980s by Shell and the 1990s by Bayer. The neonicotinoid imidacloprid is currently the most widely used insecticide in the world.
Rob’s research has focused on Bombus terrestius (buff-tailed bumbles) in particular, the species most favoured by farmers for pollination. His study involved dosing colonies with sugar water containing realistic field concentrations of neonicotinoids, and comparing the effected colonies with a control group. Unfortunately he wasn’t allowed to discuss his findings yet, because his research has not yet undergone peer review.
However, he did tell us plenty about research studies carried out by other scientists, and how pesticides work.
The LD-50 test
When the Department for Environment, Food and Rural Affairs (Defra) decides if a pesticide is safe for use, it uses the ‘LD-50’ benchmark. If a certain dose of pesticide kills 50% or above of the test subject, for example bee colonies, it is not approved for use; but at levels 49% or under dying the pesticide can be approved.
So Defra is only looking to see what percentage of bees in their test studies die, typically over a fairly short time period. But in real life, bees are not necessarily killed outright by exposure to neonicotinoids, but instead suffer olfactory memory side-effects such as difficulty learning and remembering fruitful food sources. This ‘olfactory memory’ issue has been shown in research carried out in laboratory controlled conditions; now we need more research in the field to force governments to take it seriously.
So far, most pesticide research required by governments before they approve a pesticide for use is done as short, sharp acute exposure studies. In reality, out in our towns and country-side, colonies are foraging over long time periods and face combinations of pesticides used in conjunction with each other by different gardeners or farmers.
One pesticide might not cause acute problems, but what happens when bees pick up multiple doses from several places? When each forager returns to the hive she regurgitates some of her nectar to share with her sisters (trophallaxis), so what one bee receives many others quickly do too. Experiments using coloured nectar have found that within 24 hours of nectar being brought back by just ten foragers 50% of the colony had the nectar within their honey stomach.
Neonicotinoids and pyrethroids together
Rob proudly told us that Dr Richard Gill, Postdoctoral Research Assistant at the University of Holloway, has just had his paper ‘Combined pesticide exposure severely affects individual- and colony-level traits in bees‘ published in the king of journals, Nature. In conjunction with two colleagues, Richard studied how being exposed to the combination of two pesticides (neonicotinoid and pyrethroid) at concentrations that could approximate field-level doses affected Bombus terrestius bumbles.
Some of the bumble colonies in their study were fed sugar water with the two pesticides in, but no pollen, and fitted with tiny RFID tags to track their foraging activities. The pesticide dosed group came back with less pollen than the control group. The team also found that the pesticides increased worker mortality, leading to significant reductions in brood development and colony success.
Inspecting helps varroa reproduce?
There was a lot of lively discussion and questions from the audience afterwards. One man introduced himself as a “natural beekeeper and scientist” and then went on to suggest that inspecting hives causes varroa to reproduce more quickly. He reckons that varroa reproduce best at lower temps than the 34-35°C (93-94°F) temps the bees strive to keep their brood nest at – so by opening the hive, beekeepers cause the temperature to be lowered, helping the varroa out. I wanted to investigate his theory further, and found this information on scientificbeekeeping.com –
“Avoid shade and keep colonies warm and dry. There are several reports of colonies faring better against mites when kept out in the open. Rosenkranz (1988) found that varroa prefer relatively cool temperatures of 75-88°F, well below the central brood nest temperature of 95°F. Harris, et al. (2003) state that “research by others has shown that high temperatures and extremes in relative humidity within the broodnest of a colony of bees will reduce the number of varroa mites that lay eggs.”
Hmm, our colony is in the shade, but not much we can do about that as the whole Ealing apiary is in the shade. Without trees the risk of vandalism would probably go up considerably. But is opening a hive up for a short time period really going to cool the bees down substantially? I am very skeptical about this. The advice from Beebase and our bee inspectors is to inspect regularly, and I don’t want to lose my bees to AFB/EFB or risk them swarming.
A gardening tip I heard at the meeting: use nemotode worms as an organic form of pest control. No slug pellets please!
- Neonicotinoid insecticides and bees: The state of the science and the regulatory response (Defra, Sept 2012).
Defra took a fresh look at the effects of neonicotinoid pesticides, following the publication of several new studies in 2012 suggesting that low doses of neonicotinoid insecticides can have sub-lethal effects on bees with consequences for bee populations.
They concluded that none of the studies gives unequivocal evidence that sub-lethal effects with serious implications for colonies are likely to arise from current uses of neonicotinoids. However, they have decided to update the process for assessing the risks of pesticides to bees in the light of recent research developments. The new process should include the development of a new risk assessment for bumble bees and solitary bees, alongside an updated risk assessment for honey bees.